Influence of different O₂/H₂O ratios on He atmospheric pressure plasma jet impinging on a dielectric surface

Abstract

A two dimensional (2D) axisymmetric fluid model is built to investigate the effect of different O2 and H2O admixture on the plasma dynamics and the distribution of reactive species in He atmospheric pressure plasma jet (APPJ). The increase of O2: H2O ratio slows down both the intensity and the propagation speed of ionization wave. Due to the decrease of both H2O ionization rate and H2O Penning ionization as well as the stronger electronegativity of O2, the increase of O2: H2O ratio results in a significant reduction of electron density in the APPJ, which restricts the occurrence of electron collision ionization reactions and inhibits the propagation of plasma. The excitation energy loss of O2 is not the reason for the weakening of the plasma ionization wave. The densities of O2+, O- and O2- increase with the rise of O2 admixture while H2O+ decreases due to the decrease of electron density and H2O concentration. OH- density is affected by both the increase of O- and the decrease of H2O so it shows peak in the case of O2: H2O=7:3. O is mainly produced by the excitation reactions and the electron recombination reaction (e + O2+ → 2O), which is directly related to the O2 concentration. OH is mainly produced by e + H2O → e + H + OH so the OH density decreases due to the decrease of electron density and H2O concentration with the increase of O2: H2O ratio. On the dielectric surface when the propagation of streamer extinguishes, O flux shows an upward trend while the OH flux decreases, and the propagation distance of O and OH decreases with the increase of O2: H2O ratio.

Hierarchical Structures Formed in an Atmospheric Pressure Plasma Jet by Polymerization from an Aerosol of Oxalic Acid Stabilized WO3–x Nanosheet Colloids: Toward High-Performance Electrochemical Devices and Sensors

“…Reductions in OH band intensity have been described previously for plasmas with high water content, as appears to be the case for this work, owing to the rapid quenching of OH radicals and a decrease in electron temperature. 32,36,37 No carbon lines could be resolved, suggesting that the level of dissociation of oxalic acid within the plasma gas phase was relatively low.…”

Repetitive pulsed gas–liquid discharge in different atmospheres: from discharge characteristics to plasma–liquid interactions

“…9,36 NO and NH are highly reactive with short lifetimes, thus the corresponding emission spectra are difficult to detect. Limited water vapor in the middle region creates a rather pure N 2 environment, preventing the small amount of NO and NH from being consumed (reaction (24) and ( 25)), allowing NO (A-X) and NH (A-X) spectra to be produced (Table 2). 35 Electron density and energy are the key influencing factors to the plasma properties.…”

“…Another significant influencing factor in the gas-liquid discharge is the Penning ionization between energetic metastable species and molecules such as H 2 O. 23,24 The energy of metastable Ar (Z11.5 eV) is much lower than that of the metastable He (Z19.8 eV), thus it's difficult for Penning ionization to provide sufficient seed electrons for selfsustained discharge, causing the electron avalanche to develop strongly and finally generate the maximum current in the Ar discharge. For charge transfer at the falling edge, one must take into account the memory effect, which is very common in repetitive pulsed discharge.…”

Effect of CF4 additive on dynamic surface charge deposited on dielectric by helium atmospheric pressure plasma jet

“…Material surfaces can be directionally functionalized by adding trace chemical components into the fed noble gases. APPJs with proper trace additive agents, such as oxygen, nitrogen, water vapor, and fluorocarbon, can generate abundant active molecules onto targets, enabling multiple surface functions at a higher efficiency [5][6][7][8][9][10].…”